Actually that was way too impossible for me to leave him there. I also agree that it is way too early for him .
That is not rescuing but placing him from one possible unfortunate situation into another. Give ore information why you thought that this was a good ide and why the "breeder" let him go. If he cannot stay with his mom, find a foster mother (a dog) that will adopt him with her own litter. Some shelter have their pregnant and lactating female in foster care.
He needs at least 5 more weeks with a litter and mom for nourishment and live lessons that we as humans cannot give him.
Deja, GSD, sable WL, female, born 11 / 2013
Cam, Rough Collie, sable, male, born 8/2015